This invention relates to the preparation of polyether polymers, and more particularly to the preparation of polymers of closely controlled molecular weight by a simple and reliable method.
Various types of aromatic polyethers, including polyetherimides, polyethersulfones, polyetheretherketones, and polyetherketones, have become important as engineering resins by reason of their excellent properties. These polymers are typically prepared by the reaction of salts of dihydroxyaromatic compounds, such as bisphenol A disodium salt, with dihaloaromatic molecules such as bis(4-fluorophenyl) sulfone, bis(4-chlorophenyl) sulfone, the analogous ketones and bis(halophenyl)bisimides or bis(nitrophenyl)bisimides as illustrated by 1,3-bis[N-(4-chlorophthalimido)]benzene. Substantially equimolar proportions of the two reagents are normally required, with adjustment if desired for the presence of endcapping reagents such as 1-[N-(4-chlorophthalimido)]-3-(N-phthalimido)benzene.
According to U.S. Pat. No. 5,229,482, polyether polymers are prepared by the above-described reaction in a solvent of low polarity such as o-dichlorobenzene and in the presence of a catalytically active amount of a phase transfer catalyst which is substantially stable at the temperatures employed, such as a hexaalkylguanidinium halide. A similar method of preparation, employing a monoalkoxybenzene such as anisole as solvent, is described in U.S. Pat. No. 5,830,974.
One difficulty in the preparation of polyether polymers by this method is the preparation of polymers of controlled and desired molecular weights. Since very nearly equimolar proportions of the principal reagents are required in all instances, it is typically very difficult to predict or control the molecular weight of the polyether polymer. For example, polyetherimides having weight average molecular weights in the ranges of about 43,000-46,000 and about 50,000-55,000 may be desired by reason of their advantageous properties, but a given reaction may afford a product whose molecular weight is much higher or, more often, much lower. That product, being off specification, must be discarded, increasing the cost and size of the waste stream, with adverse consequences to the environment.
It is highly desirable, therefore, to develop a method for preparing polyether polymers which is adapted to the close control of molecular weight by relatively simple means.